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Insert Molding and Encapsulation

Adding inserts to your molded part, also known as encapsulation, is an excellent way to add strength and stiffness to your finished product without sacrificing weight or flexibility. Romeo RIM’s signature thermoset polyurethane is an excellent choice for insert molding. Its lower molding temperature and pressure when compared to other materials eliminates the risk of inserts such as metal and wood becoming damaged during the molding process.

Romeo RIM’s reaction injection molding (RIM) technology provides the opportunity for a wide variety of encapsulations – anything from simple additions such as metal rods and plates to complex electronic components. The options are practically limitless. Add inserts to your next project today to create a stronger, more durable part than ever before!

The Insert Molding (Encapsulation) Process

Insert molding, variantly known as encapsulation or multi-material molding (MMM) can be carried out in a number of ways. Smaller encapsulations may be placed into the mold and molded around via a traditional process. However, special variations on traditional molding can be used when particularly large inserts, a particularly high number of inserts, or multiple dissimilar materials are needed for a part. The three most common varieties of insert molding are multi-component injection molding, multi-shot injection molding, and overmolding.

Multi-component injection molding occurs when multiple materials (such as metal and plastic, or thermoset polymer and thermoplastic) are injected into a mold simultaneously. The materials mold around one another, creating a strong “sandwich-like” structure with excellent adhesion. This process is also referred to as co-injection molding.

Multi-shot injection molding is a process in which materials are injected into the mold one at a time in a specific sequence. This creates an aesthetically and structurally pleasing “layered” geometry, which also features strong bonds between materials similar to multi-component molding. This variety of molding is also known as sequential injection molding.

Overmolding is a molding variant in which a material (usually a polymer resin) is layered on top of an existing molded component. This creates a design which features varying geometric layers around a central core structure. Overmolding can often be carried out using standard injection molding or RIM equipment, while multi-component and multi-shot injection molding require specialized tools. Romeo RIM’s technologies and materials, particularly polyurethane, are especially known for creating high-quality overmolded parts and products.

Regardless of the process used, it is important to properly prepare your insert before beginning molding. Hollow inserts must have their ends sealed using thermoplastic end caps. All inserts must be cleaned and roughened to promote good adhesion with the materials. In some cases, it is recommended to treat the insert with an adhesion promoter before molding.

Always observe the recommended minimum distance between an insert and the mold wall. For solid materials, the recommended distance is 1/8 inch (approximately 3mm) while for foamed materials it is ¼ inch (6.3mm).

Benefits of Insert Molding

The primary benefit of insert molding is the addition of strength and stiffness to the finished product. Insert molded products provide the same strength and durability while allowing a decrease in wall thickness versus parts which do not contain inserts. Products with reinforcing inserts are able to absorb higher amounts of stress when compared with those without. They also experience significantly less thermal expansion than their non-insertion counterparts.

In addition, insert molding can be a cost- and time-effective process. Adding inserts allows you to save on the cost of the more expensive thermoset materials. It also creates longer-lasting products with a higher wear resistance, saving money in both the long and short term.

Specific types of inserts also feature their own unique benefits in addition to the increased strength and stiffness caused by the encapsulation process.

Metal Stiffening Inserts

Metal encapsulations can range from flat plates and extrusions to tubes and bars. In addition, a variety of types of metal can be used as inserts, including but not limited to brass, stainless steel, bronze, aluminum, copper, nickel, and nickel alloy.

Choosing metal as an insert provides the greatest increase in strength and stiffness of the finished product. It also decreases or eliminates the thermal elongation, deflection and corrosion of the metal inserts themselves.

When encapsulating a metal insert, it is important to match the center of gravity of the insert to the center of gravity of the RIM molded material. This eliminates the possibility of warping even when temperature increases cause the polyurethane material to enter a state of compression and the metal insert to enter a state of tension.

Wood Stiffening Inserts

Wood inserts can be a cost-effective alternative to metal while still providing similar increases in strength and stiffness of the part. However, it is important to ensure wood inserts are as dry as possible before beginning the encapsulation process. An ideal moisture content for a wooden insert is below 6%.

To ensure that your wood inserts are properly dry, either dry them thoroughly before inserting them into the mold or seal them with a lacquer to prevent unwanted moisture absorption.

Threaded Inserts

Threaded inserts are an excellent choice for parts which require frequent assembly and disassembly. These inserts can be either press-fit or molded-in. Press-fit inserts are less strong but come with less risk of potential tool damage. Molded-in inserts provide greater pullout strength, as a skin forms over the entire insert surface. It is important to consider factors such as insert design, hole diameter, part density, and screw size when deciding which type of threaded insert is right for your part.

In conclusion, inserts are a cost-effective way of stiffening and strengthening your injection molded part. Various types of inserts come with their own benefits and drawbacks, so contact Romeo RIM today for help deciding just which insert is right for your next project!